PROJECT SUMMARY/ABSTRACT Autism spectrum disorder (ASD) likely has multifactorial causes, yet most epidemiological studies have studied single risk factors rather than combinations of potential causal factors. Air pollution and gestational diabetes mellitus (GDM) are two common exposures associated with ASD. Although several investigations have found associations with diverse regional pollutant exposure, the effect of the near-roadway air pollution (NRAP) mixture, which has toxicological effects relevant to pathogenesis of autism, has been less well studied. There is also uncertainty to the age-specific window of air pollution vulnerability that would provide clues to the mechanism of effects based on neurodevelopmental timing. Systemic oxidative stress and inflammation potentially affecting brain development may mediate effects of both NRAP and GDM on the developing brain, and these biological pathways may be involved in the pathogenesis of ASD. However, to our knowledge, there has been no previous study examining the joint (synergistic) effects of GDM and air pollutant exposures on ASD. Aims of this study are to assess prenatal, trimester-specific and early life windows of vulnerability to NRAP and co-pollutant effects on ASD (Aim 1) and to determine whether GDM increases the risk of ASD associated with NRAP (Aim 2). The primary resource for the study is a pregnancy-birth cohort of 450,000 mother-offspring pairs born between 1995 and 2014 in Kaiser Permanente Southern California (KPSC) hospitals; we have previously found associations of maternal GDM with offspring ASD in this cohort. KPSC is a rich resource of standardized, validated algorithms for diagnosis of GDM and ASD, recorded in a high quality electronic medical record (EMR) also providing extensive covariate information. Electronically-recorded residential address history at each visit will allow NRAP exposure assignment that will exploit changing address and, in a large cohort subset, in utero maternal workplace exposure to disentangle developmental window-specific effects. In an innovative Aim 3, electrophilic markers of NRAP and other pollutant exposures and of oxidative stress will be measured in archived neonatal dried blood spots (DBS) in a KPSC sample informatively selected based on GDM and NRAP exposure (N=300). Associations of biological markers with NRAP and GDM exposure and with ASD-relevant subclinical neurodevelopmental outcomes, identified by a review of each EMR, will be examined. Additional pathways will be explored in an untargeted ?adductome? of responses in the DBS. The study has potential to address gaps in our understanding of the role of air pollution in ASD and of biological pathways responsible. Air pollution and GDM are common risk factors that could account for a substantial proportion of ASD, if effects were found to be synergistic, and they are amenable to intervention targeting public policy and behavior. In future study the approach to investigating effects of diverse early life exposures based on the DBS adductome can be scaled up to study a broad range of multifactorial causes of ASD in the KPSC cohort.